Method of truing gears



Aug. 29, 1933. R. B. FEHR METHOD OF TRUING GEARS Filed Jan. 15, 1931 3Sheets-Sheet 1 INVENTOR B y Wu ATTORNEY5 Aug. 29, B EH METHOD OF TRUINGGEARS Filed Jan. 15, 1931 3 Sheets-Sheet 2 NVENT f7 v 77 a 4-7 ATTORNEYSAug. 29, 1933. R. B. FEHR METHOD OF TRUING, GEARS 3 Sheets-Shet 5 FiledJan. 15, 1931 ATTORN EYS Patented Aug. 29, 1933 UNITED STATES 1,924,736METHOD or 'r iUiNG GEARS Roy B. Fehr, Detroit, Mich assignor, by mesneassignments, to Detroit Trust Company, Detroit, Mich, a corporationof-Michigan Application January 15, 1931. Serial No. 508,825

4 Claims.

The present invention relates to a method of truing gears or otherbodies of similar shape, and is an improvement on the method disclosedin the patent to Copland et al No. 1,683,867 granted September 11, 1928.

My co-pending application Serial No. 508,652, filed January 14, 1931,discloses a method of gear truing in which the gear tooth faces areabraded by means of a lap having a form complemental to that of thegear, and in which the gear is maintained in telescopic engagement withthe lap.

throughout the truing operation so that the lap ping operation maybeperformed in a machine driven at a relatively high rate of speed, thegrinding operation being continuous and uninterrupted.

The object of the present invention is to provide a high speed method ofthe character above referred to by which a very uniform grinding actionis obtained on the tooth faces throughout the length and breadth thereofby rigidly holding both the gear and lap against relative tiltingmovement while permitting one to have limited lateral movements duringthe lapping operation. With the above and other objects in view theinvention may be said to comprise the method and apparatus asillustrated in the accompanying drawings hereinafter described andparticularly set forth in the appended claims together with suchvariations and modifications thereof as will be apparent to one skilledin the art to which the invention appertains.

Reference should be had to the accompanying drawings form'rg a part ofthis specification in which:

Figure l is a side elevation of a machine embodying this invention.

Figure 2 is a front elevation of the machine shown in Figure 1.

Fig. 3 is a plan view of the lap and its support, a portion of thesupport being broken away and shown in section.

Fig. 4 is a section taken on the broken line indicated at 4-4 in Fig. 3.

Fig. 5 is a side elevation showing the machine in which a floatingsupport for the gear is provided.

Fig. 6 is a section taken on the line indicated at 6-6 in Fig. 5.

Fig. '7 is a side elevation support.

Fig. 8 is a section taken on the line indicated at 8-8 in Fig. 6.

Referring first to Figures 1 to 4 of the drawings, the lapping machineis provided with a of the gear arbor disposed vertically. At the topthereof the frame 1 has a laterally projecting portion 6 which overhangsthe turntable 3 in which is slidably mounted a vertically disposedspindle 7 which is disposed substantially in axial alignment with theturntable 3 and lap 5. The gear 8, to be lapped, is adapted to berigidly secured to the lower end of the spindle '7 for telescopicengagement with the lap 5. At its upper end, the spindle 7 hasdetachably secured thereto a spline extension Slrvvhich is provided withstraight or helically disposed ribs or teeth which are engaged by aspline guide 10 which has internal ribs or teeth of 0drresponding formand which is detachably secured to the frame. The helical angle of thespline is such as to impart to the gear exactly the same rotary movementwhich would be imparted to it by the lap if the gear were movedlongitudinal- 1y through the lap with the lap held against turningmovements. 1

The longitudinal lead of the spline teeth is exactly the same as that ofthe gear teeth, and for gears of small helix angle a spline extensionand guide having teeth disposed at a small helix angle will be required.When the gear is a spur gear its helix angle ls zero and a splineextension and spline guide having straight teeth will be employed. j Thespindle '7 is adapted to be reciprocated axially by means of a lever 11which is pivotally connected at its forward end to a collar 12 rotatablymounted on the spindle '7 and held against longitudinal movement withrespect thereto. The lever 11 is connected intermediate its ends to theframe 1 by means of a floating pivot 13 and is connected at its rear endby means of a connecting rod 14 with the crank arm 15 of a crank shaft16 journalled in the frame 1. The shaft 16 may be driven by any suitablemeans to oscillate the lever 11 and reciprocate the spindle 'Z. Thefloating pivot l3 is mounted on amovable pivot carrier 17 which ispivotally mounted on an eccentric 18 carried by a shaft 19 which isjournalled in the frame 1. The shaft 19 is provided with a hand crank 20by means of which the eccentric 18 may be turned to raise or lower thepivot carrier 17.

During oscillation of the lever 11 the carrier 1'? is free to swinglaterally on the eccentric 18 through an angle sufficient to allow thelever 11 to have the bodily lateral movement necessary to permit theforward end thereof attached to the spindle 7 to move vertically in astraight line during the oscillation of the lever. The verticaladjustment of the pivot carrier 17 is sufficient to move the lower endof the spindle carrying the gear 8 from a position within the lap 5 to aposition above and clear of the lap to permit a gear to be removed fromthe spindle and replaced with another gear to be trued. The length ofthe stroke imparted to the spindle 7 by the oscillating lever ll is suchthat, when the pivot carrier 1'? is in its lowermost position, the gear8 remains in telescope engagement with the lap 5 throughout the entirestroke. Since there is no disengagement of the gear and lap during thereciprocating stroke of the spindle, the reciprocating movement may bequite rapid and the grinding action will be continuous.

The lap is preferably of a length several times the actual width of thegear and is preferably composed of a metal as hard as or harder than themetal of the gear. By reason of the hardness of the lap and by reason ofthe much greater area of the tooth faces of the lap, the rate of wearper unit of area on the lap tooth faces is but a small fraction of therate of wear on the gear tooth faces, so that a lap tooth face will notbe appreciably deformed in the process of grinding off the high spots ona contacting gear tooth face. Furthermore, passing a succession of gearsthrough a lap distributes the minute errors over all of the teeth of thelap. The teeth of the gears which are of correct form except for slightinaccuracies in some of the teeth tend to eliminate inaccuracies in thelap teeth so that the lap toothfaces are maintained substantially true.

According to the present method the lap and gear are rigidly heldagainst relative tilting movement and against turning movements withrespectto the members on which they are mounted during the lappingoperation, but the lap or gear, one or the other, is so supported thatit is free to move laterally in any direction perpendicular to its axis,so that throughout the reciprocating stroke the lap and gearautomatically center themselves with respect to each other, so thatexcessive pressure between the tooth faces during any portion of thestroke is prevented.

As best shown in Figs. 3 and 4 of the drawings, the turntable '3 isprovided with upwardly projecting guide flanges 21 to the inner faces ofwhich are secured hardened steel ball races 22 and which serve as guidesfor a laterally movable intermediate supporting member 23 to which areattached hardened steel ball races 24 which face outwardly and aredisposed opposite the ball races 22. The opposed faces of the ball races22 and 24 are provided with ball receiving grooves which extendlongitudinally thereof in'which are mounted the bearing balls 25, whichserve to accurately position the supporting member 23 and permit thesame to move freely in a lateral direction. The ball races on thesupporting member 23 are provided with wedge shims 26 which may beadjusted to adjust the ball races 24 bodily toward or away from the ballraces 22 to clamp the balls tightly between the races and take up anyplay in the bearing members. I

A lapcarrier 2'7 is mounted on top of the intermediate supporting member23 for movement lateralh in a direction at right angles to the directionof movement of the intermediate supporting member 23. The lap carrier 27has depending flanges 28 tothe inner faces of which are attached ballraces 29 which are opposed to ball races 30 secured to the intermediatesupporting member. The ball races 29 and 30 being grooved to receiveballs 31 and the ball races 30 being adjustable by means of wedge shims32 to clamp the balls snugly between the ball races. The balls 25 and 31are retained in the races 24 and 30 of the intermediate supportingmember by means of keepers 33 which are attached to the intermediatesupporting member 23 at the outer end of the ball races 24 and 30.

The lap carrier 2'? is provided on the top face thereof with an annularshoulder 34 within which lateral movement only since the lateralmovement of these members during the operation of the machine is veryslight. The lateral movements of the intermediate supporting member 23are limited by a downwardly projecting annular flange 3'? which extendsinto the opening of the annular turntable 23 and the intermediatesupporting member 23 is provided with an annular flange 38 at the topthereof which projects upwardly between the side flanges 28 of the lapcarrier 27 and an inner annular flange 39 formed on the lap carrierinwardly of the flanges 38.

In order to protect the bearings from abrasive material a sheet metalguard 40 is preferably attached to the marginal edge of the lap carrier27 and incloses the intermediate supporting member and the upper portionof the turntable 3. The lower end of the guard being of a diametersomewhat greater than the turntable 3 to allow the necessary relativelateral movement. In order to introduce abrasive carrying liquid intothe lap a suitable funnel 41 may be attached to the upper end of the lap5 through which a stream of liquid may be directed into the upper end ofthe lap and from which the liquid will flow through the spaces betweenthe lap and gear teeth.

In the operation of the machine a gear is attached to the lower end ofthe spindle 7 while the pivot carrier 1'7 is adjusted to its uppermostposition to bring the lower end of the spindle 7 to a position clear ofthe lap 5, and after the gear has been attached to the spindle, thecarrier .17 is shifted to its lowermost position to enter the gear intothe lap -5 after which the crankshaft 16 is driven to reciprocate thegear within the lap. Since the stroke of the spindle '7 is such that thegear does not move out of telescopic engage ment with the lap during thereciprocating stroke, the spindle 7 may be rapidly reciprocated toeffect a continuous and rapid abrasion of the tooth faces of the gear.After the gear and lap are telescopically engaged the turntable 3 may beadjusted by means of the hand wheel 4 through the small angle necessaryto establish abrasive contact between opposed tooth faces of the gearand lap and maintain a torsional pressure between the engaging toothfaces, and after the gear teeth have been ground sufficiently on oneside the turntable 3 may be adjusted in the reverse direction to bringthe opposite faces of the gear teeth into engagement with lap toothfaces, and the operation may, then be continued until the opposite facesof the gear teeth have been ground down the desired amount.

between the balls and raceways.

To avoid non-uniform grinding action such as -may be caused byinequalities in torsional pressure during the reciprocating stroke whichmight otherwise be caused by the mounting of a gear .in a positionslightly eccentric with respect to the lap, it is desirable that thegear and lap have a limited relative movement in a directionperpendicular to their common axis, so that there is at all times anautomatic centering of the lap with respect to the gear.

The mounting for the lap illustrated in Figs. 3 and 4 of the drawings,permits the lap to have a limited lateral movement in any directionper-,. pendicular to its axis but constrains the lap to turning movementwith the turntable on which it is mounted. If desired, however, the lapmay be rigidly supported and the gear may be so mounted on the spindlethat it is constrained to turn with the spindle but is free to movelaterally in any direction perpendicular to the axis of the spindle.Such a mounting for the gear is illustrated in Figs. 5 to 8 of thedrawings, which will now be described.

In this modification the lap is rigidly supported in the turntable 42 inaxial alignment with a vertically movable spindle 43 which is providedat its lower end with a mounting for a laterally movable arbor 44 towhich the gear is attached.

As best shown in Figs. 6, '7 and 8, spindle 43 is provided at its lowerend with an elongated head 45 which has attached to the opposite facesthereof, hardened steel ball races 46 and which serves as a guide for anintermediatesupporting member 47 which has upwardly extending guideflanges 48 which form a channel between them to receive the head 45. Theguide flanges 48 have hardened steel raceways 49 secured to the innerfaces thereof opposite the raceways 46 of the head, and the raceways 46and 49 are grooved to receive balls 50. The intermediate supportingmember 47 has downwardly extending guide flanges 51 which extend in adirection at right angles to the flanges 48 and which are integrallyjoined with the upper guide flanges 48 by corner blocks 52 which lie inthe exterior angles of the crossing channels formed by the flanges 48and 51 of the intermediate member.

Guide flanges 51 are provided on their inner faces with hardened steelraceways 53 and serve as a guide for a transversely elongated head 54 onthe upper end of the gear. carrying arbor 44, the head 54 being providedon its opposite side faces with hardened steel raceways 55 opposed tothe raceways 53 of the flanges, the raceways 53 and 55 being providedwith grooves to receive anti-friction balls 56. The raceways 49 and 53of the intermediate supporting member are provided with wedge shims 5'7which may be adjusted by means of bolts 58 to take up any play in thebearings and maintain snug engagement The balls are preferably retainedin the raceways of the intermediate supporting member by means ofkeepers 59 extending across the outer ends of the raceway grooves on theintermediate member and keepers 60 extending across the inner ends ofsaid grooves.

The lateral movements of the arbor with respect to the spindle 43 arelimited by means of interengaging members on the spindle and arbor, thespindle being provided with a recess 61 in the lower end thereof, andthe arbor being provided with a projection 62 of somewhat less diameterthan the recess which projects into the recess.

A cylindrical sheet metal housing 63 is preferably provided to enclosethe coupling members joining the spindle and arbor and protect thebearings against the entry of abrasive mav terial. The housing 63 isattached to the spindle 43, having an opening in which the spindle fitsand being supported upon the projecting ends of the head 45; The housingmay be provided with an annular bottom plate 64 which projects inwardlybeneath the projecting ends of the head 54 of the arbor 44. The internaldiameter of the annular plate 64 is slightly greater than the diameterof the arbor 44 to permit the necessary lateral play, and the gapbetween the interior of the annular plate 54 and the arbor may be closedby a flange 65 secured to the arbor and overlying the upper face of theplate 64.

In each of the modifications described, the

gear and lap are held against relative tilting movements about axestransverse to the spindle or lap axis, so that-unsymmetrical crowning ofthe ends of the gear teeth is avoided. A slightly greater pressure perunit of area may be exerted when the gear is at the ends of the lapwhich may result in slightly greater abrasion at the ends of the teethproducing a slight crowning effect which is advantageous. By the presentmethod, this crowning eifect is very slight and is alike in all teeth byreason of the fact that the gear and lap are rigidly held againstrelative tilting movements.

The relative lateral movements permitted between the lap and gear assurecorrect centering of the gear with respect to the lap throughout thelapping operation, since the movably mounted lap or gear is free tocenter itself at all times with respect to the gear or lap with which itengages, the position of the gear with respect to the lap beingdetermined by the circumferentially spaced inter-engaging tooth faces ofthe gear and lap which are held in contact under torsional pressure.

A new lap will have certain minor inaccuracies which should beeliminated prior to the use of the lap in truing of gears. Theseinaccuracies may be eliminated by lapping a considerable number of gearssuccessively in the lap. The gears employed for the truing,of the lapmay be gears which have not previously been trued but which have beenmanufactured with fair accuracy. The abrasive action of the gear teethon the lap teeth has the effect of gradually reducing and eliminatingthe errors in the lap teeth putting the lap in condition for theaccurate finishing of gears. The gears which were used for truing thelap may again be lapped either in the same lap or in another previouslytrued lap. After a lap has once been trued it may be'used continuouslyinthe truing of gears until its teeth are worn to such an extent that theydo not possess the necessary strength, and throughout the use of the lapthe teeth thereof -will be maintained substantially correct incontourand spacing by reason of the substantially uniform distribution of wearover.

the surfaces of the lap teeth and the continual 'which the abrasiveaction of the gear teeth is substantially uniform throughout the entiresurfaces of the gear teeth.

It will further be apparent that the lap and gear will not bind duringthe lapping operation and that the pressure between the contacting toothfaces will be quite uniform and will be distributed uniformly over theentire area. of the gear tooth faces.

Furthermore, it is to be understood that the particular form ofapparatus shown and described, and the particular procedure set forth;are presented for purposes of explanation and illustration and thatvarious modifications of said apparatus and procedure can be madewithout departing from my invention as defined in the appended claims.

What I claim is:

1. The herein described method of truing gears which consists intelescopically engaging a gear and lap, one of which has the form of anexternal gear and the other the form of an internal gear, the gear andlap being of the same pitch diameter and complemental in form, impartingrelative axial reciprocating movements to the gear and lap, one withrespect to the other while maintaining the gear and lap in telescopicengagement, and rigidly holding the gear and lap against relativetilting movements while permitting free lateral movement of one withrespect to the other in any direction perpendicular to the axes of thegear and lap and while main- 1 taining a torsional pressure betweenopposed tooth faces of the gear and lap.

2. The herein described method of truing gears which consists intelescopically engaging a gear and lap, one of which has the form of anexternal gear and the other the form of an internal gear, the gear andlap being of the same pitch diameter and complementalin form, impartingrelative axial reciprocating movements to the gear and lap, one withrespect to the other while maintaining the gear and lap in telescopicengagement, rigidly holding the gear and lap against relative tiltingmovements while per mitting free lateral movement of one with respect tothe other in any direction perpendicular to the axes of the gear andlap, and establishing and maintaining a torsional pressure betweenopposed tooth faces of the gear and lap by relative angular adjustmentsof the gear and lap,

one with respect to the other about their axes.

3. The herein described method of truing gears which consists intelescopically engaging a gear and lap, one of which has the form of anexternal gear and the other the form of an internal gear, the gear andlap being of the same pitch diameter and complemental in form, impartingrelative axial reciprocating movements to the gear and lap, one withrespect to the other while maintaining the gear and lap in telescopicengagement, rigidly holding the gear and lap against relative tiltingmovements while permitting free lateral movement of one with respect tothe other in any direction perpendicular to the axes of the gear andlap, establishing abrasive contact between opposed tooth faces of thegear and lap by angularly adjusting one with respect to the other, andpositively controlling relative angular movements of the gear and lapduring the relative reciprocation thereof to maintain said abrasivecontact.

4. The herein described method of truing helical gears which consists intelescopically engaging a gear and lap, one of which has the form of anexternal helical gear and the other the form of an internal helicalgear, the gear and lap being of the same pitch diameter and complementalin form, imparting relative axial reciprocating movements to the gearand lap, one withrespect to the other while maintaining the gear and lapin telescopic engagement, rigidly holding the gear and lap againstrelative tilting movements while permitting free lateral movement of onewith respect to the other in any direction perpendicular to the axes ofthe gear and lap, establishing abrasive contact between opposed toothfaces oi the gear and lap by angularly adjusting one with respect to theother, and oscillating the gear and lap, one with respect to the otherduring the reciprocation thereof, while positively maintaining a speedof relative angular movement between points on the gear and lap lying inthe pitch cylinder common to the gear and lap which is equal to thespeed of relative axial movement times the tangent of the helix angle ofthe gear and lap.

ROY B. FEHR.

